System for providing cell bus management in a switch platform including a write port cell count in each of a plurality of unidirectional FIFO for indicating which FIFO be able to accept more cell

ABSTRACT

A method and apparatus for providing cell bus management in a switch platform are provided. Each unidirectional FIFO buffer of a cell bus controller outputs a write port cell count from a write port. A cell count value is programmed at which the write port cell count is outputted. When the write port cell count indicates that the FIFO buffer can not accept additional data or cells, a master bidirectional FIFO unit ceases reading cells to a unidirectional FIFO buffer of the slave bidirectional FIFO unit in response to the write port cell count. Furthermore, the master bidirectional FIFO unit disables a corresponding switch from routing cells to the slave bidirectional FIFO unit in response to the write port cell count; the switch routes the cells to another of the slave bidirectional FIFO units. The master bidirectional FIFO unit resumes reading cells to the second unidirectional FIFO buffer of the slave bidirectional FIFO unit in response to a write port cell count indication that the FIFO buffer can accept additional data or cells. In response, the master bidirectional FIFO unit enables an associated switch to route cells to the slave bidirectional FIFO unit.

FIELD OF THE INVENTION

The present invention relates generally to the management of networknodes and, more particularly, to a mechanism for managing cell trafficin a multiservice switch platform.

BACKGROUND OF THE INVENTION

Until recently there has persisted a fundamental dichotomy betweendifferent types of telecommunication networks. A first type oftelecommunication network, the telephone network, switches andtransports predominantly voice, facsimile, and modulation-demodulationsystem (modem) traffic. A second type of telecommunication network, thedata network, switches or routes and transports data between computers.

Telephone networks were developed and deployed earlier, followed by datanetworks. Telephone network infrastructures are ubiquitous, however, andas a result data networks typically are built, to a limited extent,using some components of telephone networks. For example, the end useraccess link to a data network in some cases is implemented with adial-up telephone line. The dial-up telephone line thus connects the enduser computer equipment to the data network access gateway. Also, highspeed digital trunks interconnecting remote switches and routers of adata network are often leased from telephone carriers.

Nonetheless, telephone and data network infrastructures are usuallydeployed together with limited sharing of resources, especially withregards to the core components of the networks—the switches and routersthat steer the payloads throughout the networks. The cost of thisredundancy coupled with advances in data network technologies has led,where possible, to integrated data traffic comprising voice, data,facsimile, and modem information over a unified data network. As such, adata network should now be able to accept, service, and deliver any typeof data on a random, dynamic basis using a minimum set of hardware on asingle platform.

Multiservice network switches are used to provide a data path, orinterface, between multiple networks, each of which may operate using adifferent type of data or according to a different networking standardprotocol. Examples of the networking protocols supported by thesemultiservice switches include, but are not limited to, frame relay,voice, circuit emulation, T1 channelized, T3 channelized, andAsynchronous Transfer Mode (ATM).

Typical prior art switch platforms handling data of different types,speeds, and bandwidths exhibit a problem in that there is a significantrisk of data loss because of the different data parameters. In order toreduce the risk of data loss, the typical prior art switches usefirst-in-first-out (FIFO) buffers. The problems with the typical priorart FIFOs are numerous but, overall, can be generalized as inflexibleand performance limiting. First, the typical prior art FIFOs arelimiting in that they are unidirectional and only support data flow inone direction. Next, the interface through the typical prior art FIFO issynchronous, thereby limiting the types of data accepted by the switchplatform and the types of subscriber equipment coupled to the platform.Furthermore, the typical prior art FIFO has a fixed-width data path.

The typical prior art FIFO exhibits congestion problems in that it failsto provide adequate information regarding the quantity and contents ofthe FIFO. For example, the prior art FIFO does not provide quantitativeinformation regarding the availability of cell space in the FIFO, andthe cell space availability indications typically provided are based onword boundaries. Additionally, the prior art FIFO fails to provide a wayto discard invalid data that has been written to a FIFO. Furthermore,the typical prior art FIFO limits diagnosis and switch platformperformance monitoring as it fails to provide for a non-destructiveprocessor read of the FIFO or a diagnostic loopback between multipleFIFOs.

In addition to the aforementioned problems with typical prior art FIFOs,these FIFOs fail to provide fair rate-based bandwidth allocation amongcell traffic sources. Instead, the typical prior art FIFOs use around-robin priority scheme to service the traffic sources, wherein alltraffic sources are serviced in consecutive order with equal bandwidthbeing allocated to each traffic source. In a wide area network, forexample, bandwidth allocation is important because customers areserviced and charged according to the bandwidth used. Therefore, abandwidth allocation scheme that provides equal bandwidth to all trafficsources regardless of source requirements is inefficient and costineffective.

Furthermore, the typical prior art FIFO is problematic in that it failsto provide adequate cell traffic congestion management, a failure thatresults in dropped and lost cells. Furthermore, the prior art FIFOinefficiently manages the routing of information through a switchplatform. This inefficiency results from globally assigning the cell buslogical connection number (LCN) and the UDF the same value for eachconnection. This global assignment tightly couples the LCN address spaceand the UDF address space, thereby forcing a large portion of the cellbus address space to be unusable. Furthermore, this global assignmentrequires switch platform software to make queries to multiple switchcards to find an unallocated value for use in both the LCN and the UDFaddress spaces.

SUMMARY AND OBJECTS OF THE INVENTION

It is therefore an object of the invention to provide fair rate-basedcell traffic arbitration and bandwidth allocation between multiple celltraffic sources.

It is a further object of the invention to prevent dropped or lost cellsin a switch platform by providing cell bus traffic congestionmanagement.

It is a further object of the invention to provide flexibility and aperformance improvement in the translation of cell traffic routinginformation.

These and other objects of the invention are provided by a method andapparatus for providing cell bus management in a switch platform. Eachunidirectional FIFO buffer of a cell bus controller outputs a write portcell count from a write port. A cell count value is programmed at whichthe write port cell count is outputted. When the write port cell countindicates that the FIFO buffer can not accept additional data or cells,a master bidirectional FIFO unit ceases reading cells to aunidirectional FIFO buffer of the slave bidirectional FIFO unit inresponse to the write port cell count. Furthermore, the masterbidirectional FIFO unit disables a corresponding switch from routingcells to the slave bidirectional FIFO unit in response to the write portcell count; the switch routes the cells to another of the slavebidirectional FIFO units. The master bidirectional FIFO unit resumesreading cells to the second unidirectional FIFO buffer of the slavebidirectional FIFO unit in response to a write port cell countindication that the FIFO buffer can accept additional data or cells. Inresponse, the master bidirectional FIFO unit enables an associatedswitch to route cells to the slave bidirectional FIFO unit.

Furthermore, each unidirectional FIFO buffer outputs a status indicatingspace available in the corresponding unidirectional FIFO buffer for atleast one more cell. When the space available status indicates thatspace is not available in the FIFO buffer for at least one more cell,the master bidirectional FIFO unit ceases reading cells to theunidirectional FIFO buffer of the slave bidirectional FIFO unit inresponse to the space available status. The master bidirectional FIFOunit disables a corresponding switch from routing cells to the slavebidirectional FIFO unit in response to the space available status; theswitch routes the cells to another of the slave bidirectional FIFOunits. The master bidirectional FIFO unit resumes reading cells to thesecond unidirectional FIFO buffer of the slave bidirectional FIFO unitin response to a status indicating space is available in the FIFObuffer. In response, the master bidirectional FIFO unit enables anassociated switch to route cells to the slave bidirectional FIFO unit.

Other objects, features, and advantages of the invention will beapparent from the accompanying drawings and from the detaileddescription which follows below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements, and in which:

FIG. 1 is a multi-service switch platform of one embodiment. The switchplatform comprises two Processor/Switch Modules (PSMs).

FIG. 2 is a switch platform of one embodiment as a stand alone node.

FIG. 3 shows switch nodes of one embodiment connected as a networkthrough router interfaces.

FIG. 4 shows switch nodes of one embodiment connected as a networkthrough ATM interfaces.

FIG. 5 is a switch of one embodiment as a node in a BPX/IPX network.

FIG. 6 is a system block diagram of the switch platform of oneembodiment.

FIG. 7 is a PSM comprising Cell Bus Controllers (CBCs) of oneembodiment.

FIG. 8 is a cell format of the QE mode of one embodiment.

FIG. 9 is a cell format of the ATM mode of one embodiment.

FIG. 10 is a block diagram of a Cell Bus Controller (CBC) of oneembodiment.

FIG. 11 is a diagram of an egress data flow of a CBC of one embodiment.

FIG. 12 is a diagram of an ingress data flow of a CBC of one embodiment.

FIG. 13 is a block diagram of an Egress Cell Input Controller (ECIC) ofone embodiment.

FIG. 14 is a block diagram of an Egress Cell Processor (ECP) of oneembodiment.

FIG. 15 is a block diagram of a Multicast Engine (MCE) of oneembodiment.

FIG. 16 is a block diagram of a Cell Bus Master (CBM) of one embodiment.

FIG. 17 is a block diagram of a Cell Bus Slave (CBS) of one embodiment.

FIG. 18 shows the CBM cell bus signal timing of one embodiment.

FIG. 19 shows the CBS cell bus signal timing of one embodiment.

FIG. 20 is a block diagram of an Ingress Cell Processor (ICP) of oneembodiment.

FIG. 21 is a block diagram of an Ingress Cell Output Controller (ICOC)of one embodiment.

FIG. 22 is a flowchart of a method for routing at least one cell in aswitch platform of one embodiment.

FIG. 23 is an address map RAM data field definition of a CBC of oneembodiment.

FIG. 24 is a mapping for a first PSM card in a first slot of oneembodiment.

FIG. 25 is a mapping for a second PSM card in a second slot of oneembodiment.

FIG. 26 is a service module configuration of one embodiment in whichservice module A communicates with service module B.

FIG. 27 is a service module configuration of one embodiment in which aservice module fails and a redundant service module is on the same CBCas the failed service module.

FIG. 28 is a service module configuration of one embodiment in which aservice module fails and a redundant service module is on a differentCBC from the failed service module.

FIG. 29 is a parameterized bi-directional synchronous cell FIFO withloopback and processor access interface implemented in the CBC of oneembodiment.

FIG. 30 lists the configuration parameters of the bidirectional FIFOs ofa CBC of one embodiment.

FIG. 31 lists the input/outputs (I/Os) and a corresponding interfacedescription for the bi-directional FIFOs of a CBC of one embodiment.

FIG. 32 is a flowchart for controlling cell traffic in a switch platformof one embodiment.

FIG. 33 is a block diagram of the flag generation of one embodiment.

FIG. 34 is a timing diagram of a write port of one embodiment.

FIG. 35 is a timing diagram of a read port of one embodiment.

FIG. 36 is a flowchart for providing cell bus management in a switchplatform of one embodiment.

FIG. 37 is a timing diagram of a processor port of one embodiment.

FIG. 38 is a bandwidth distribution of one embodiment using a parallelresistor network model.

FIG. 39 is a flowchart for providing cell traffic arbitration in aswitch platform of one embodiment.

FIG. 40 is a block diagram of an interface loopback of one embodiment.

FIG. 41 is a block diagram of an individual cell bus loopback of oneembodiment.

DETAILED DESCRIPTION

Intended advantages of the invention described herein may comprise theprovision of synchronous parameterized FIFO memory functions forbi-directional data flow through a switch platform, asynchronous readand write ports in a unidirectional FIFO, a FIFO having a programmablecell size, and a FIFO having a programmable word size, but theembodiment is not so limited. Furthermore, intended advantages maycomprise the provision of a FIFO that provides quantitative informationbased on cell boundaries regarding the availability of cell space in theFIFO, a way to discard invalid data written to a FIFO, a non-destructiveprocessor read of a FIFO, and a diagnostic loopback between multipleFIFOs, but the embodiment is not so limited.

FIG. 1 is a multi-service switch platform 100 of one embodiment. Theswitch platform 100 comprises two Processor/Switch Modules (PSMs)102-104. Each PSM 102-104 is coupled to communicate between a backplane110 and eight service modules (SMs) 120-154, but the embodiment is notso limited. The outside interfaces provided by the service modules120-154 and the PSMs 102-104 provide the user a large selection ofinterfaces at speeds from DS0 modem access to OC3 ATM interfacecomprising T1/E1, DS3, OC3, modem, and router communications, but theembodiment is not so limited. The PSM cards 102-104 provide high speednative ATM interfaces through the backplane 110, wherein the interfacescomprise T3, OC3, and OC12 interfaces which can be configured as ATMports or trunks, but the embodiment is not so limited. In oneembodiment, the PSMs 102-104 support switched connections betweenservice module ports and between PSM back card ports. The PSMs 102-104are coupled to the service modules 120-154 using a service moduleinterface with the physical layer convergence function performed on thePSM. The PSM embodiments support 1.2 Gbps, 15 Gbps, and 45 Gbps therebyallowing support for each of these rates on the same switch node, butthe embodiments are not so limited. The higher capacity PSM embodimentsmay be deployed in configurations where there are broadband interfacesin the network, and trunks can be supplied from a broadband interface.

The switch platform 100 of one embodiment supports applicationsrequiring a combination of switching, routing, and other interfacefunctions. As such, the switch platform may stand alone or function aspart of a larger network. Therefore, the switch platform describedherein may be configured either as a routing node or a feeder nodeattached to a router node, but the embodiment is not so limited. As arouting node, the platform will support AutoRoute and PNNIsimultaneously.

FIG. 2 is a switch platform 200 of one embodiment as a stand alone node.Furthermore, multiple nodes can be coupled to form a network. Thetrunking of the nodes can be through the ATM interfaces 202 provided onthe service modules of each switch platform, the ATM interfaces providedon the PSM 204, or a wide variety of interfaces, for example, a 100 mbsEthernet connection provided through the router interface. FIG. 3 showsswitch nodes 302-306 of one embodiment connected as a network throughrouter interfaces 312-316. FIG. 4 shows switch nodes 402-406 of oneembodiment connected as a network through ATM interfaces 412-416.Furthermore, the ATM interfaces on the switch nodes of one embodimentprovide ATM native connections to other types of network switches. FIG.5 is a switch platform 502 of one embodiment as a node in a BPX/IPXnetwork 504.

FIG. 6 is a system block diagram of the switch platform 600 of oneembodiment. As previously discussed herein, the switch platform 600comprises two PSMs 602-604 and sixteen service modules, wherein twoservice module front cards 606-608 each comprise four service modulesand two service module back cards 610-612 each comprise four servicemodules, but the embodiment is not so limited. The PSMs 602-604 provide,but are not limited to, the following functions: switch fabric;processor; cell bus interface to service modules; clocking; ethernet andRS232 ports; and system environment monitoring. The PSMs 602-604 providea shared memory switch fabric capable of sustaining two times OC12bandwidth. Furthermore, the PSMs 602-604 provide the switch platform 600control functions and a switch fabric for intra-nodal cell switching.Moreover, the PSMs 602-604 provide a variety of interfaces forsatisfying trunk requirements. In one embodiment, the system bandwidthmay be increased by changing the PSM, thereby allowing for the use ofmultiple high bandwidth service modules.

The service modules of one embodiment support services including, butnot limited to, Internet Protocol (IP), frame relay (FR), circuitemulation, and ATM. The narrow band interfaces, or service modules,supported in one embodiment comprise, but are not limited to, eight portchannelized and unchannelized T1/E1 frame relay service modules, eightport T1/E1 ATM service modules, and four port circuit emulation.Furthermore, supported service modules comprise eight port CO-FRAD,eight port T1/E1 circuit emulation, T3/E3 circuit emulation, two port16M HSSI FR, two port DS1 and DS0 channelized DS3 FR, two port DS3unchannelized DS3 FR, two port 52M HSSI FR, ATM service modules, andvoice card service modules. Moreover, broadband interfaces, or servicemodules, are supported.

In one embodiment, each PSM supports 128 k cell storage within theswitch, but the embodiment is not so limited. In one embodiment, thetotal bandwidth on the switch is more than two OC12, wherein thebandwidth is partitioned for local switching and for trunk switching.Local switching refers to switching between service modules of a switchplatform while trunk switching refers to switching between a PSM trunkand either the service modules or the PSM trunk. Alternate embodimentsmay support an aggregate of 24 Gbps bandwidth.

Eight cell buses are supported by each PSM of one embodiment. Each cellbus is capable of sustaining one OC3 bidirectional bus; however, the PSMmay support a two times clock mode providing more than OC6 capacity. Thecell buses provide a high speed interface between the switch fabric andthe service modules using a Cell Bus Controller ASIC (CBC ASIC or CBC).The CBC interfaces with the eight OC3 cell bus lanes provided by thePSM. To facilitate communication between PSMs, a cell bus slave is addedto each PSM. In one embodiment, the cell bus slave on a first PSM of theswitch platform is coupled to one of the cell buses driven by a secondPSM of the switch platform. Therefore, a PSM may send a cell back toitself through the switch. In one embodiment, the local switchingfunction supports 16K bi-directional connections, and the trunkswitching function supports 32K bi-directional connections, but theembodiment is not so limited.

The cell bus of one embodiment comprises a number of buses that provideinter-connectivity and redundancy to the switch modules. In particular,the cell bus provides a high speed cell data path between the servicemodules and the PSM switch fabric. The cell bus comprises a collectionof independently controlled bus lanes. Each of the bus lanes, orsub-cell buses, provides up to two OC3 bandwidth, wherein a total offour cell bus lanes are provided for each sub-shelf. The four cell buslanes, where each is capable of supporting one OC3 bandwidth, allows theembodiment to sustain two times OC12 bandwidth. Furthermore, two sets ofcell bus lanes are provided for supporting service module redundancy.

The switch platform software of one embodiment comprises severalsoftware subsystems distributed across the PSM and the service modules.The software subsystems are separated into three layers: node managementsoftware; network control software; and platform control software.Subsystems in each of these layers are separated by applicationprogrammer interfaces (APIs). A virtual switch interface (VSI) serves asa standardized interface on the switch thereby allowing one controllerimplementation to be used across different platforms for the samefunction. The switch platform of one embodiment supports VSI slaves forPNNI, AutoRoute, and tag switching. Within a switch platform,VSI-related functions are performed by one or more processors known asVSI slaves. The VSI slaves may be organized using a centralized model, adistributed model and a hybrid model; each of these models may besupported by the platform of one embodiment, but the embodiment is notso limited.

FIG. 7 is a PSM 700 comprising Cell Bus Controllers (CBCs) 702-704 ofone embodiment. Each CBC 702-704 controls cell traffic between four CellBus Masters (CBMs) CBM0-CBM7, one Cell Bus Slave (CBS) CBS0-CBS1, andtwo Queue Engine ASICs (QE ASIC or QE) 712-714, but the embodiment isnot so limited. It is noted that, as used herein, the term “ingress” isused to refer to cell traffic flow toward the switch 712-714, or QE, andthe term “egress” is used to refer to cell traffic flow away from theswitch 712-714. Thus, the cell traffic flow from the QE 712-714 to theCBC 702-704 is termed egress, and the cell traffic flow from the CBC702-704 to the QE 712-714 is termed ingress. The CBC 702-704, in actingas a master to four cell buses and a slave to one cell bus, controlscell traffic between the five cell buses and the two QEs 712-714. A CBCinterface couples the CBCs 702-704 and the QEs 712-714. In oneembodiment, a CBC can handle 32 devices on the CBC interface, but theembodiment is not so limited.

The CBC of one embodiment supports one OC-12 (622 Mbit/s) cellinput/output (I/O) bandwidth, meaning that the CBC can read/write a cellfrom/to the QE within approximately 680 nanoseconds, but the embodimentis not so limited. Each CBM supports an OC-3 bandwidth for transmittingand receiving. The CBC of one embodiment may implement cell storageusing first-in-first-out (FIFO) buffers along the cell datapath. The CBCis used twice in the QE mode in each PSM card. Each CBC receives cellsover a bus from one QE but sends cells over the bus to both QEs. Onegress, the CBC routes traffic to the CBS.

Each CBM of one embodiment comprises clock logic, which can operate ateither 21 MHz, 42 MHz, or 50 MHz, and a clock input pin, but theembodiment is not so limited. Moreover, all four CBMs can runsynchronously on one common clock. Each CBS of one embodiment handlesbus traffic of speeds up to OC-3; therefore, the aggregate bandwidth forthe cell buses is more than one OC-12. Each CBS of one embodiment runson a 21 MHz, 42 MHz, or 50 MHz clock, but the embodiment is not solimited.

The CBC of one embodiment supports two modes, a QE mode and an ATM mode.In supporting the QE mode, the CBC utilizes two transmit and two receiveslave ports of the CBC interface. The CBC interface uses a 16-bit datapath that transmits cells that each comprise twenty-seven 16-bit words.FIG. 8 is a cell format of the QE mode of one embodiment. The two CBCinterface slave ports, which have separate control signals and onecommon datapath, are used to send cells to the two QEs, where data issent to only one QE at a time. The transmit slave port is used toreceive cells from one QE.

In supporting the ATM mode, one CBC interface receive slave port and oneCBC interface transmit slave port are used, but the embodiment is not solimited. The CBC interface comprises an 8-bit datapath that transmitscells that each comprise 56 byte words. FIG. 9 is a cell format of theATM mode of one embodiment. Egress traffic is routed to the CBS in theATM mode.

FIG. 10 is a block diagram of a Cell Bus Controller (CBC) 1000 of oneembodiment. FIG. 11 is a diagram of an egress data flow of a CBC 1000 ofone embodiment. FIG. 12 is a diagram of an ingress data flow of a CBC1000 of one embodiment. The CBC 1000 comprises, but is not limited to,an Egress Cell Input Controller (ECIC) 1002, an Egress Cell Processor(ECP) 1004, a Multicast Engine (MCE) 1006, a CBM 1008, a CBS 1010, anIngress Cell Processor (ICP) 1012, and an Ingress Cell Output Controller(ICOC) 1014.

FIG. 13 is a block diagram of an Egress Cell Input Controller (ECIC) ofone embodiment. In operation the ECIC receives cells from one QE 1302,using the cell bus transmit slave interface. As such, the ECIC is thefirst module of one embodiment through which incoming cells pass on theegress datapath of the CBC. The primary interfaces of the ECIC are withthe QE or ATM 1302 and the ECP 1304. The ECIC is responsible forinterfacing with the QE/ATM 1302 over a cell bus interface, wherein theQE/ATM 1302 is the cell bus transmit master and the ECIC is the cell bustransmit slave. Furthermore, the ECIC stores ATM cells sent by the QE1302 in a two-cell deep FIFO 1306, and provides ATM cell availabilitystatus to the ECP 1304. Moreover, the ECIC converts the 16-bit inputdatapath in the QE mode, or the 8-bit input datapath in the ATM mode, toa 32-bit internal datapath.

FIG. 14 is a block diagram of an Egress Cell Processor (ECP) of oneembodiment. The ECP is the second module of one embodiment through whichincoming cells pass on the egress datapath of the CBC. The primaryinterfaces of the ECP are with the ECIC 1402, the MCE 1404, the CBS,four CBMs 1408, and the ICOC 1410. The ECP processes cells received fromthe QE via the ECIC 1402 and forwards the cells to one of four CBMs1408, a CBS, or an MCE 1404. Processing includes Cell Bus Header look-upfrom the Cell Bus Header RAM 1412 for cell bus traffic and Multicast(MC) Address RAM 1414 lookup for multicast traffic. For ATM traffic, theECP simply forwards the cell to the CBS, without the Cell Bus Headerlook-up. The ECP unloads cells from the ECIC input FIFOs and checks theparity of the data read from these FIFOs.

The ECP performs cell bus interface polling address to target addressmapping using thirty-two possible polling address destinations that aremapped to twenty-six targets. The mapping is performed by Address MapRAM 1416 look-up logic, wherein the targets are the service modules viaa CBM, a second PSM Card via a CBS, and a MCE.

For cell bus cells in the QE mode of one embodiment, the ECP generates aCell Bus Header (CBH) random access memory (RAM) address for the cellsusing a logical connection number (LCN), accesses the CBH RAM for theCBH entry, and generates a new Logical Slot ID in the CBH, wherein thephysical slot ID is found in the Address Map RAM. Furthermore, the ECPadds the CBH to the cells and sends the cells to one of the CBMs or theCBS, depending on the address. If the number of cells in the egress FIFOof the target reaches a threshold, the ECP discards the incoming cell.The threshold is defined as the maximum number of cells in the FIFO, 8cells in one embodiment, with a 2-bit threshold configurationsubtracted, but the embodiment is not so limited.

For MC cells in the QE mode of one embodiment, the ECP uses the uppertwelve bits of the LCN to perform Multicast Address Look-up. The ECPreplaces the first UDF in the cell with the MC Record RAM Address andsends the cells to the MCE. If a back pressure signal from the MCE isactive, the cell is discarded by the ECP.

In the ATM mode of one embodiment, cells are routed to the CBS withoutany processing, except for a parity check. When a loopback control isactive, all traffic is routed to the ICOC. When the cell availablesignal from the ICOC is inactive, the cell is discarded. Any parityerror in the cell header will cause the cell to be discarded, while anyparity error in the payload will set an error flag but will not causethe cell to be discarded.

FIG. 15 is a block diagram of a Multicast Engine block (MCE) of oneembodiment. The MCE and the associated queues comprise the third modulethrough which MC cells pass on the egress datapath of the CBC. Theprimary interfaces of the MCE are with the ECP 1502, the ICP, and theICOC 1504. The MCE is responsible for storing MC cells in either thecritical 1506 or the non-critical queue 1508, replicating and sending MCcells for each LCN in a given MC Group at a rate of up OC-12 to the ICOC1504. The MCE sends cells to the ICOC 1504 when the ICP has no cells tosend. The MCE provides queue storage for thirty-two cells, of whichsixteen are critical cells and sixteen are non-critical cells. The MCEreplicates MC cells for each LCN associated with that PSM card in agiven MC Group at a rate of up to OC-12, and inserts a 5-bit target slotID, read from a MC record RAM 1510, into the fourth word of the cell.The MCE sends replicated cells to the ICOC 1504 when datapath grants aregiven by the ICP, and generates back pressure to the ECP 1502 wheneither of the critical 1506 or non-critical queues 1508 reach athreshold that is configured by firmware.

FIG. 16 is a block diagram of a Cell Bus Master (CBM) 1600 of oneembodiment. The CBM 1600 interfaces with the cell bus 1602 as a master;as such, the CBM 1600 handles cell traffic in both ingress and egressdirections.

The CBM 1600 is used four times in the CBC of one embodiment, but theembodiment is not so limited.

The CBM 1600 and associated FIFOs 1610-1612 are used to handle bothingress and egress cell bus traffic. During data ingress, the CBM 1600arbitrates requests from service modules on the cell bus 1602 and grantsone service module the right to send a cell in the next cell time. Inarbitrating, the CBM 1600 provides polling and bandwidth specificarbitration logic to determine which service module can send cells tothe CBM 1600. The CBM grant logic grants CBM access to the servicemodule selected so the service module can send a cell to the CBM 1600.In supporting data ingress, the CBM 1600 provides a dedicated eight-cellingress FIFO 1612 for storing a maximum of eight cell bus cells, but theembodiment is not so limited. The CBM 1600 interfaces with the ICP viathe CBM ingress FIFO 1612; the CBM 1600 writes to the ingress FIFO 1612while the ICP reads from the FIFO 1612 and processes the read cell. TheCBM 1600 checks parity over each 8-bit word as the word is read from thecell bus 1602, converts the received cell to a 32-bit word, and writesthe 32-bit word into the ingress FIFO 1612. Moreover, the CBM 1600checks the slot ID of the cell received against the slot ID of theservice module that was granted access to the CBM 1600 in order toverify that the correct service module is sending the cell. The CBM 1600polls for status comprising back pressure, ready, and present status,but the embodiment is not so limited.

During data egress, the CBM 1600 provides a dedicated 8-cell egress FIFO1610 for storing a maximum of eight cell bus cells. The ECP writes tothe FIFO 1610 while the CBM 1600 reads from the FIFO 1610. The CBM 1600reads 32-bit words from the egress FIFO 1610 and checks parity over eachof the two 16-bit words read. The CBM 1600 converts each 16-bit word totwo 8-bit words and generates parity. Each 8-bit word and thecorresponding parity is provided to the cell bus 1602. As the read cellis transmitted to all service modules on the cell bus 1602, each servicemodule will read in the cell and determine if the cell is destined forthat service module by looking at the broadcast field and the slot IDfield in the Cell Bus Header. The CBM 1600 checks to make sure a servicemodule acknowledges receipt of the transmitted cell. The CBM 1600 hasthe capability to reset each service module.

FIG. 17 is a block diagram of a Cell Bus Slave (CBS) 1700 of oneembodiment. The CBS 1700 interfaces with the cell bus 1702 as a slave,wherein the CBS 1700 and associated FIFOs 1710-1712 are used to handleboth ingress and egress cell bus traffic. The CBS 1700 interfaces withthe ECP and the ICOC. On ingress, the CBS 1700 receives cells from thecell bus 1702, wherein the CBS 1700 provides a dedicated 16-cell ingressFIFO 1712 for storing a maximum of 16 cell bus cells. The CBS 1700writes to the FIFO 1712 while the ICP reads from the FIFO 1712.Furthermore, the CBS 1700 checks parity over each 8-bit word as the wordis read from the cell bus 1702. The CBS 1700 checks the Slot ID and theMC bit in the Cell Bus Header of the cell received against the Slot IDof the CBS 1700 and accepts the cell if the Slot ID matches or the MCbit is asserted; otherwise, the cell is discarded. As a cell isreceived, the cell is converted to a 32-bit word before being writteninto the ingress FIFO 1712. An acknowledge signal is sent to thetransmitting CBM after the cell is received. The accepted cell iswritten to the CBS ingress FIFO 1712. The ICP reads the cell from theingress FIFO 1712 and processes the cell.

On egress, the CBS 1700 is responsible for providing a dedicated 8-cellegress FIFO 1710 for storing a maximum of eight cell bus cells. The ECPwrites to the egress FIFO 1710 while the CBS 1700 reads from the egressFIFO 1710. The CBS 1700 converts a 32-bit word read from the egress FIFO1710 to two 16-bit words, and checks parity over each 16-bit word. TheCBS 1700 makes a request to an associated CBM during a poll phase tosend a cell to the cell bus 1702, and waits for a grant. If a grant isreceived, the CBS 1700 sends the cell to the cell bus 1702 and the CBM.Furthermore, the CBS 1700 generates ready, present, and back pressurestatus. Moreover, on egress the CBS 1700 provides the capability toloopback egress cell traffic, wherein the loopback provides cell trafficto ingress for diagnostic individual cell bus loopback. FIG. 18 showsthe CBM cell bus signal timing of one embodiment. FIG. 19 shows the CBScell bus signal timing of one embodiment.

FIG. 20 is a block diagram of an Ingress Cell Processor (ICP) of oneembodiment. The ICP is the second module through which incoming cell buscells pass on the ingress datapath of the CBC. The primary interfaces ofthe ICP comprise the four CBMs, the CBS, the ICOC 2004, and the MCE2002. The ICP is responsible for determining service decisions byarbitrating between four CBMs and one CBS. Once the service decision isdetermined, a cell is then read from the FIFO of the selected source andprocessed. If the CBC is in the QE mode, the ICP will do a look-up inthe external LCN RAM for the LCN and insert it into the cell. Noprocessing is done in the ATM mode of one embodiment, but the embodimentis not so limited. An ACP, or processor, can manipulate the priority ofCBS traffic by setting a 6-bit CBS priority configuration. The ICPunloads cell bus cells from the ingress cell bus FIFO of the selectedsource, and checks parity over the data read from the input FIFO.

In the QE mode, the ICP removes the Cell Bus Headers from the cell buscells and forms a new cell. The ICP generates LCN RAM addresses, looksup LCNs in the external LCN RAM using the generated address, inserts thenew LCN in the new cell, extracts the target slot ID from the Cell BusHeader and inserts it into the new cell, and transmits the generated newcells to the ICOC.

In the ATM mode, the ICP transfers the cell to the ICOC after a paritycheck. When there is no cell to send in a cell time, the ICP grants theMCE the cell time so the MCE can send the cell to the ICOC.

FIG. 21 is a block diagram of an Ingress Cell Output Controller (ICOC)of one embodiment. The ICOC is the last module through which ATM cellspass on the ingress datapath of the CBC, but the embodiment is not solimited. The primary ICOC interfaces comprise the interfaces with theICP module, the ECP module, the MCE module, and the QE 2102 or ATM. TheICOC determines the QE destination from the target slot ID and sendscells to that QE using the cell bus receive slave interface.

The ICOC stores ATM frames sent by the MCE, the ICP, or the ECP into thetwo-cell FIFO 2104. The ICOC interfaces with the ingress QE/ATM 2102over a cell bus interface. Furthermore, the ICOC converts the 32-bitinternal datapath to a 16-bit interface datapath in the QE mode, and toan 8-bit interface path in the ATM mode.

An ACP interface and control logic is responsible for handling ACPrequests to the CBC. The primary interfaces of the ACP interface andcontrol logic are with the external ACP sub-system and the CBC internalmodules. The ACP interface and control module is responsible formonitoring the ACP interface and looking for valid CBC requests from theACP. The ACP interface and control module maintains various control andstatus registers, and provides configuration information to the CBC.Furthermore, the ACP interface and control module performs ACP-requestedactions and passes the required information to the appropriate module sothat it can complete the operation.

Cell bus logic controls cell bus cell flow to and from the five externalcell buses of one embodiment. The cell bus logic is implemented in theCBM and the CBS. Each of the four CBMs of one embodiment control anassociated cell bus. The CBS can interface with one of the four cellbuses controlled by the four CBMs or it can communicate with a dedicatedcell bus. In the PSM, the CBS communicates over a dedicated cell bus.Furthermore, the CBS is connected to the cell bus which is controlled bya CBM in another PSM card; this is how the two PSMs communicate witheach other.

When the CBM grants a slave module request to send a cell to therequesting slave module during the next cell time, it presents the grantaddress and asserts a grant enable bit from cell bus cycle 51 to cycle58. When the slave receives its Physical Slot ID on the grant bus alongwith the asserted grant enable signal any time during the grant cycle,the slave is enabled to transmit a cell onto the bus during the nextcell time.

In the operation of a slave module sending data to a CBM, when the slavemodule which has made a request to send a cell to the CBM receives thegrant from the CBM, the slave module starts sending the cell at thebeginning of the next cell bus frame time following assertion of theTx-Frame signal at cycle 1. The first byte of the cell is sent to theCBM at cycle 1, while the last byte of the cell is sent at cycle 56.

As the CBM is receiving data from the slave module, the CBM checks tosee if the cell is coming from the slave module to which the grant wasprovided during the last cell bus frame time. If a mis-comparisonoccurred, an error condition is indicated. The CBM also checks forparity on each byte of the cell as it is received into the CBM.

In the operation of one embodiment of a CBM sending data to slavemodules, the first byte of a cell is transmitted in two cycles, cycle 58and cycle 1. When the CBM is ready to send a cell to the slave module,it will begin sending the cell starting at the last cycle of the currentcell bus frame time, cycle 58. The first byte of the cell is sent outagain at the first cycle of the next cell bus frame time, cycle 1. Thesecond byte of the cell is sent out in cycle 2, while the last byte ofthe cell is sent out in cycle 56. In cycle 57, the CBM sends out allzero data. Parity generation is performed on all cell data bytes.

In one embodiment, transmitted cells are sent to all slave modules onthe cell bus. Each slave module must read in the first byte of the celland determine if the cell is addressed to the slave module. As such, theslave module determines whether the physical slot ID field in the firstbyte of the cell matches the physical slot ID of the slave modulereceiving the cell, or determines whether the MC bit in the first byteof the cell is a 1. If either of these conditions are satisfied the cellis read and processed; otherwise, the cell is discard.

The slave modules can send three types of status to the CBM, but theembodiment is not so limited. The three types of status are sent usingthe poll bits like the slave module requests, wherein the poll bits areasserted at different cycles for each different status. The three typesof status comprise: a ready status, wherein the slave module is workingand ready to interface with the CBM; a present status, wherein the slavemodule is present but may not be ready; and a stop status, wherein theslave module is congested and cannot accept any more cells from the CBM.

The CBC of one embodiment provides cell bus traffic congestionmanagement between the CBMs and the CBSs of a switch platform. Inperforming cell traffic congestion management, a CBS determines that itis congested and is running out of buffer space to store the incomingcells. The congested CBS informs, or back-pressures, the correspondingCBM to stop sending cells to the congested CBS. The back-pressurenotification uses a back-pressure bit defined in the cell bus interfacefor each service module on a cell bus. When the back-pressure bit isasserted for a service module, the CBC will prevent the QE from sendingcells to that service module. This notification should be sent beforethe CBS FIFO is full and completely runs out of space to store incomingcells so as to provide time for the CBM to react while providing enoughstorage space for the cells already in transit to the CBS. Upon receiptof the notification from the CBS, the CBM ceases transmission of cellsto the congested CBS. The congested CBS will update the congestionnotification to the CBM when the CBS ceases to be congested. The CBM, inturn, continuously monitors the congestion notification and resumessending cells to the CBS when the CBS ceases to be congested.

In order to provide the traffic management function without adding moresignals to the cell bus, the congestion notification is performed usingan existing request and status poll signal. When the CBS is congested itwill assert a poll signal at cell bus cycle 50, when the CBS is in anodd slot of the cell bus frame, or cycle 56, when the slave is in aneven slot of the cell bus frame. In one embodiment, CBS congestion isindicated when the CBS input FIFO has space for less than eight cells,wherein the eight cells handle CBM reaction latency and cells already intransit, but the embodiment is not so limited. Upon receipt of thecongestion notification by the CBM, the CBM forwards the congestionnotification message to the ECP. As a result, the ECIC blocks celltransmission to the CBC ASIC.

The CBC of one embodiment provides flexibility and performanceimprovement in the translation of routing information between source andtarget service modules. In the QE mode the CBC supports CBH look-up inthe ingress direction, or cell bus to QE direction, and the egressdirection, or QE to cell bus direction. The CBH RAM contains one primaryand one alternate CBH for each of the 64K logical connection numbers(LCNs). The logical organization of the RAM is 128K×17, but theembodiment is not so limited.

In operation, cells are routed among service modules by the CBC using afirst memory to convert an address having a first format into an addresshaving a second format. In one embodiment, the address having the firstformat is received in a header of a cell, and the address formatcomprises a 17-bit cell bus logical connection number of a destinationport. The address having the second format is a 16-bit UDF used by aswitch of the switch platform. The address having the first format isused to form a third address that is used to access the first memory.The data located at the third address of the first memory is a 16-bitUDF used to address the switch.

A second memory is used to convert an address having the second formatinto an address having the first format. The address having the secondformat is used as a fourth address to access the second memory. The datalocated at the fourth address of the second memory is a 32-bit cell busheader that addresses a destination port. The destination port is atleast one service module of the switch platform. The first and secondmemory comprise an external random access memory, but the embodiment isnot so limited.

In one embodiment, each connection of a service module has a 17-bit cellbus LCN comprising a 12-bit LCN, a 4-bit Slot ID, and a cell bus number.As the QE, or the switch, has a 16-bit UDF, a mapping is used to mapbetween the LCN and the UDF. The mapping is used because when a cell istransmitted to the CBM on ingress to be switched by the QE, the 17-bitcell bus LCN is converted to the 16-bit UDF used by the QE. Followingswitching, when a cell is enroute to the target service module onegress, the 16-bit UDF is converted to the 17-bit cell bus LCN for thetarget service module. The conversions in both the ingress and theegress direction are performed by the CBC via an external RAM lookup.The CBC uses two external memory structures, the CBH RAM and the LCNRAM.

On cell ingress, the 12-bit cell bus LCN and the 4-bit Slot ID from thecell bus Header of the incoming Cell Bus cell are extracted.Furthermore, the cell bus number, indicating whether the cell is comingfrom CBM 0, 1, 2, 3, or the CBS, is formed by mapping a 3-bit cell bussource number to a 1-bit cell bus number. This mapping may be programmedby firmware. The 12-bit LCN, 4-bit Slot ID, and the cell bus number areused to form a 17-bit address to access the external LCN RAM. The datafrom the LCN RAM is the 16-bit UDF and it is forward along with the cellto the QE.

On cell egress, the 16-bit UDF of the incoming QE cell is used as theaddress for the external CBH RAM. The data of the CBH RAM is a 32-bitCBH. It is added to the cell and sent to the service module.

FIG. 22 is a flowchart of a method for routing at least one cell in aswitch platform of one embodiment. Operation begins at step 2202, atwhich a logical connection number and a slot identification areextracted from a first cell header of a cell received from at least oneservice port. A cell bus number is formed, at step 2204, by mapping acell bus source number of the first cell header. A first address isformed, at step 2206, from the logical connection number, the slotidentification, and the cell bus number. The first address may comprisea 17-bit address, but the embodiment is not so limited. A first externalmemory is accessed using the first address, at step 2208. A 16-bit UDFis read from the first external memory, at step 2210, and the UDF isforwarded to the switch, at step 2212.

Furthermore, a cell may be routed from a switch to a service module, orport, by addressing a second external memory, or CBH RAM, using a 16-bitUDF of at least one cell received from a switch. A second cell header isread from the second external memory, and the second cell header isadded to the cell. The second cell header may comprise 32

bits, but the embodiment is not so limited. The second cell along withthe second cell header is sent to a destination service port.

The CBC of one embodiment provides 1-to-1 and 1-to-N service moduleredundancy. Therefore, when any service module in the system fails, aredundant module can be brought on-line to replace the failed module.This redundancy is provided using two CBCs having a total of 128K ofCell Bus Headers and supporting 64K connections. For each connection,there is a primary CBH entry in one CBC, and an alternate CBH entry inthe other CBC. The contents are the same but the addresses of these twoCBHs are different by one bit, the alternate bit. Each service modulehas an alternate bit. When a new connection is made, the firmware adds aprimary CBH entry to the CBC that currently has the target servicemodule, and adds an alternate CBH entry to the other CBC; this is doneto make sure CBH information is on both CBCs. The firmware chooses whichof the two CBH entries to use by setting the alternate bit in theAddress Map RAM.

FIG. 23 is an address map RAM data field definition of the CBC of oneembodiment. Up to two PSM cards are supported in two slots of a switch,but the embodiment is not so limited. A set of mappings is defined and,based on the mappings, the firmware programs an Address Map RAM and theCell Bus Master Configuration Registers. FIG. 24 is a mapping for afirst PSM card in a first slot of one embodiment. FIG. 25 is a mappingfor a second PSM card in a second slot of one embodiment.

FIG. 26 is a service module configuration of one embodiment in whichservice module A (SM A) communicates with service module B (SM B). Inthis example, SM A and SM B are controlled by the same CBC CBC1, buteach SM could be controlled by different CBCs. When one service modulesends cell traffic, or traffic, to another service module, the trafficgoes through a series of steps in being routed. The primary CBH entry isused. The cell traffic is received by the CBC controlling the sourceservice module. In the CBH, the 5-bit Target Slot ID specifies thetarget service module. The CBC looks into the QE destination register tofind out to which QE the traffic should be routed; the traffic is thenrouted to that QE. Once the current QE receives the cell traffic, itwill forward the cell traffic to the proper CBC, depending on its LCNentry; the CBC uses an address to index into the Address Map RAM forthis information. The CBC uses the LCN number to get the CBH from theCBH RAM. When a service module fails, the redundant service module canbe either on the same CBC or on another CBC.

FIG. 27 is a service module configuration of one embodiment in which aservice module SM B fails and the redundant service module D (SM D) ison the same CBC CBC1 as the failed service module SM B. When SM B fails,the redundant SM D takes over, wherein SM D is controlled by the sameCBC CBC1 as SM B. In replacing SM B with SM D, SM D is initialized withthe information resident in SM B, and the Address Map RAM is changed sothat the address for SM B is now pointing to SM D.

FIG. 28 is a service module configuration of one embodiment in which aservice module SM B fails and the redundant service module C (SM C) ison a different CBC CBC2 from the failed service module. When SM B fails,the redundant SM C takes over, wherein SM C is controlled by a differentCBC CBC2 than SM B. In replacing SM B with SM C, SM C is initializedwith the information resident in SM B. In CBC1, the QE-destinationregister is modified to have traffic to SM B forwarded to QE2. In CBC2,the Address Map RAM is modified to have traffic intended for SM Bforwarded to SM C. In CBC2, the Address Map RAM is modified to use thealternate CBH entry. In CBC2, the QE-destination register is modified tohave traffic to SM A forwarded to QE1.

In one embodiment, each CBC supports 26 devices comprising 24 cell busservice modules (8 service modules per cell bus), a PSM Card, and aMulticast Engine, but the embodiment is not so limited. As thecorresponding firmware and software deals with the CBC devices in a5-bit Logic Slot ID, a mapping of Logical Slot ID to Cell Bus Number andPhysical Slot ID is used, but the embodiment is not so limited.Furthermore, the firmware and software transmits cells to the CBC ASICvia the QE. As the QE Chip has 16 polling addresses, another level ofmapping is used.

A parameterized bidirectional synchronous cell FIFO with loopback andprocessor access interface is used for the ingress and egress FIFOs ofboth the CBM and the CBS, as described herein, but the embodiment is notso limited. The FIFO of one embodiment provides synchronousparameterized first-in first-out memory functions for bi-directionaltraffic. FIG. 29 is a parameterized bi-directional synchronous cell FIFO2900 with loopback and processor access interface implemented in the CBCof one embodiment. A two-port REG_FILE 2902 is used as the memory block,wherein the REG_FILE 2902 is synchronous write and asynchronous read. Anasynchronous interface is used for communication between the read 2904and the write domain 2906, wherein the read ports and the write ports ofeach uni-directional FIFO are asynchronous to each other. The read andwrite logic is controlled by the clock of their respective domains2904-2906. Programmable parameters are used to customize the FIFO 2900,wherein the cell size, or number of words per cell, and the word size,or number of bits per word, are both programmable, or parameterized.FIG. 30 lists the configuration parameters of the bi-directional FIFOsof the CBC of one embodiment. FIG. 31 lists the input/outputs (I/Os) anda corresponding interface description for the bi-directional FIFOs ofthe CBC of one embodiment.

Specifically, the parameterized bidirectional FIFO unit controls celltraffic in a switch platform using a first and a second unidirectionalFIFO buffer. The first and second unidirectional FIFO buffers eachcomprise asynchronous read and write ports. A cell size of the first andsecond unidirectional FIFO buffers is programmable. Furthermore, a wordsize of the first and second unidirectional FIFO buffers isprogrammable. The bi-directional FIFO unit is coupled to write at leastone cell from and read at least one cell to at least one asynchronoustransfer mode (ATM) interface, at least one frame relay interface, atleast one voice interface, and at least one data interface, but theembodiment is not so limited. As such, the first unidirectional FIFObuffer is coupled to write at least one cell from an ATM interface, aframe relay interface, a voice interface, and a data interface. Thefirst unidirectional FIFO buffer is coupled to read at least one cell toat least one switch, wherein the switch handles cells from sourceshaving a number of bandwidths. The switch is coupled to route the atleast one cell to an OC12 trunk line and to at least one service module.The service module is coupled to provide the cell to at least oneservice subscriber using T1, E1, T3, E3, OC3, and OC 12 ports, but theembodiment is not so limited.

The second unidirectional FIFO buffer is coupled to read at least onecell to an ATM interface, a frame relay interface, a voice interface,and a data interface. Furthermore, the second unidirectional FIFO bufferis coupled to write at least one cell from at least one switch, whereinthe switch handles cells from sources having a number of bandwidths. Theswitch may be coupled to route the cell from an OC12 trunk line and froma service module. The service module is coupled to provide the cell toat least one service subscriber using T1, E1, T3, E3, OC3 , and OC 12ports, but the embodiment is not so limited. Invalid cells may bediscarded from each unidirectional FIFO buffer, but the embodiment isnot so limited.

FIG. 32 is a flowchart for controlling cell traffic in a switchplatform. Operation begins at step 3202, at which a cell size of each ofa first and second unidirectional FIFO buffers is programmed. A wordsize of each of the first and second unidirectional FIFO buffers isprogrammed, at step 3204. At least one cell is asynchronouslytransferred among a number of ports having a number of bandwidths, atstep 3206. The asynchronous transfer uses a bidirectionalfirst-in-first-out (FIFO) unit, wherein the bidirectional FIFO unitcomprises a first and a second unidirectional FIFO buffer. Invalid cellsare discarded from each unidirectional FIFO buffer, at step 3208. Anon-destructive read is executed of the bidirectional FIFO unit, at step3210, while cells are being written to and read from the bidirectionalFIFO unit.

The step of asynchronously transferring may comprise the steps ofsynchronously writing the cell from a port to the first unidirectionalFIFO buffer, and synchronously reading the cell from the firstunidirectional FIFO buffer to at least one switch, wherein the readingis asynchronous with the writing, but the embodiment is not so limited.Furthermore, the step of asynchronously transferring may comprise thestep of synchronously writing at least one cell from the switch to thesecond unidirectional FIFO buffer, and synchronously reading the cellfrom the second unidirectional FIFO buffer to a port, wherein thereading is asynchronous with the writing, but the embodiment is not solimited.

In one embodiment, two signals pass through the asynchronous interface,a write_port increment_read_cell_counter signal, and aread_port_decrement_write_cell_counter signal. As both of these signalsare pulses, an asynchronous edge finder is used on each of thesesignals, but the embodiment is not so limited. The asynchronous edgefinder of one embodiment is implemented in three steps. The first stepis to make sure the pulse is long enough to be captured. If the signalis going from a fast-clocked register to a slow-clocked register, inorder to ensure that the slow-clocked register captures the pulse, thefast-clocked register holds the value for a certain number of cycles.The number of cycles that the value is held is the ratio of the fastclock to the slow clock. For example, if the fast clock is 50 MHz (20 nsperiod) and the slow clock is 21 MHz (48 ns), then the signal needs tobe held for three cycles (20 ns* 3=60 ns>48 ns). This would ensure thatthe slow-clocked register captures the signal. Signals going from aslow-clocked register to a fast-clocked register do not have to dealwith this issue. The second step handles meta-stability usingdoubling-latching logic. The third step is to capture the edge, whereinsimple logic is used to make sure the signal is valid for one cycle inthe destination clock domain.

The CBC of one embodiment supports high level flags comprising cellavailable flags and cell space available flags. FIG. 33 is a blockdiagram of the flag generation of one embodiment. The flags are based oncell boundaries rather than word boundaries, but the embodiment is notso limited.

A write port of the FIFO uses two counters: a write_word_counter, and awrite_cell_counter. The write_word_counter counts the number of wordsthat have been written in a cell. The write_cell_counter counts thenumber of cells currently in the FIFO. When a whole cell is written intothe FIFO, the write_word_counter resets to zero, the write_cell_counteris incremented by one. A signal is sent through the asynchronousinterface to notify the read port to increment its read_cell_counter.The space_available flag is based on cell boundaries. If there is onecell space left in the FIFO, as soon as the first word is written intothe FIFO, the space_available signal will be turned off. If the FIFO isfull, the illegal_write signal will prevent the write_address registerfrom incrementing.

In operation, each unidirectional FIFO buffer of one embodiment outputsa write port cell count from a write port. In one embodiment, a cellcount value is programmed at which the write port cell count isoutputted. When the write port cell count indicates that the FIFO buffercan not accept additional data or cells, the master bidirectional FIFOunit ceases reading cells to the unidirectional FIFO buffer of the slavebidirectional FIFO unit in response to the write port cell count.Furthermore, the master bidirectional FIFO unit disables a correspondingswitch from routing cells to the slave bidirectional FIFO unit inresponse to the write port cell count; the switch routes the cells toanother of the slave bidirectional FIFO units. The write port logic ofeach unidirectional FIFO buffer is synchronous with a write clock,wherein the write clock operates at a frequency substantially equal to50 megahertz, but the embodiment is not so limited.

The master bidirectional FIFO unit resumes reading cells to the secondunidirectional FIFO buffer of the slave bidirectional FIFO unit inresponse to a write port cell count indication that the FIFO buffer canaccept additional data or cells. In response, the master bidirectionalFIFO unit enables an associated switch to route cells to the slavebidirectional FIFO unit.

In addition to the write port cell count, each unidirectional FIFObuffer of one embodiment outputs a status indicating space available inthe corresponding unidirectional FIFO buffer for at least one more cell.When the space available status indicates that space is not available inthe FIFO buffer for at least one more cell, the master bidirectionalFIFO unit ceases reading cells to the unidirectional FIFO buffer of theslave bidirectional FIFO unit in response to the space available status.Furthermore, the master bidirectional FIFO unit disables a correspondingswitch from routing cells to the slave bidirectional FIFO unit inresponse to the space available status; the switch routes the cells toanother of the slave bidirectional FIFO units.

The master bidirectional FIFO unit resumes reading cells to the secondunidirectional FIFO buffer of the slave bidirectional FIFO unit inresponse to a status indicating space is available in the FIFO buffer.In response, the master bidirectional FIFO unit enables an associatedswitch to route cells to the slave bidirectional FIFO unit.

FIG. 34 is a timing diagram of a write port of one embodiment. Thewrite_enable 3402 and write_data 3404 inputs are registered on the writeclock 3406. An internal writ_address points to the next address to bewritten.

Each unidirectional FIFO buffer of one embodiment outputs a read portcell count from a read port. The read port cell count is a statusindicating space available in the corresponding unidirectional FIFObuffer for at least one more cell. The read port logic of eachunidirectional FIFO buffer is synchronous with a read clock. The readclock may operate at a frequency substantially equal to 21 megahertz or42 megahertz, but the embodiment is not so limited.

A read port of the FIFO uses two counters, a read_word_counter, and aread_cell_counter. The read_word_counter counts the number of words thathave been read in a cell. The read_cell_counter counts the number ofcells currently in the FIFO. When a whole cell is read from the FIFO,the read_word_counter resets to zero, and the read_cell_counter isdecremented by one. A signal is sent through the asynchronous interfaceto notify the write port to decrement the write_cell_counter. Thecell_available flag is on cell boundaries. If there is one cell left inthe FIFO, as soon as the first word is read from the FIFO, thecell_available signal is turned off. If the FIFO is empty, theillegal_read signal will prevent the read_address register fromincrementing.

FIG. 35 is a timing diagram of a read port of one embodiment. Theread_enable input 3502 is registered on the read clock 3504. TheREG_FILE already has the next read data available at its output. Oncethe registered read_enable signal 3502 is active, it will load the datainto the read_data_out register. This is the reason for the two clockdelays between the read_enable signal 3502 going active and dataappearing on the read_data_outport.

FIG. 36 is a flowchart for providing cell bus management in a networkswitch of one embodiment. Operation begins at step 3602, at which a cellcount value is programmed at which a first slave bidirectional FIFO unitoutputs a write port cell count. A determination is made, at step 3604,as to whether the cell count of the slave bidirectional FIFO unitexceeds the programmed cell count value. If the cell count exceeds theprogrammed cell count value, the write port cell count is output fromthe first slave bidirectional FIFO unit. The reading of cells to thefirst slave bidirectional FIFO unit is suspended, at step 3606, inresponse to the write port cell count. Cells are routed to a secondslave bidirectional FIFO unit in response to the write port cell count,at step 3608, in response to the suspended reading to the firstbidirectional FIFO unit. The rerouted cell is read to the second slavebidirectional FIFO unit in response to the write port cell count. If thewrite port cell count of the first slave bidirectional FIFO isdetermined not to exceed the programmed cell count value, or when thewrite port cell count drops back below the programmed cell count value,reading of the at least one cell to the first slave bidirectional FIFOunit is resumed, at step 3610. Cell bus management in the network switchof one embodiment further comprises outputting a read port cell count,and outputting from at least one read port a status indicating spaceavailable in a unidirectional FIFO buffer for at least one more cell.

Cell bus management in the network switch of one embodiment furthercomprises outputting a status indicating space available for at leastone more cell from a first slave bidirectional FIFO unit when a cellcount of at least one slave bidirectional FIFO unit exceeds one. Readingof at least one cell to the first slave bidirectional FIFO unit issuspended in response to a status indicating no space available. Thecell is routed to a second slave bidirectional FIFO unit in response toa status indicating no space available. The rerouted cell is read to thesecond slave bidirectional FIFO unit. When the status of the first slavebidirectional FIFO unit again indicates space available in the bufferfor at least one more cell, the routing of the at least one cell to thesecond slave bidirectional FIFO unit is disabled, and reading to thefirst slave bidirectional FIFO unit is resumed.

A processor port allows a processor to perform a non-destructive readfor any address in the FIFO when such action is granted by the readport. A diagnostic interface of the bidirectional FIFO unit supports thenon-destructive read of the bidirectional FIFO unit while at least onecell is being written to and read from the bidirectional FIFO unit. Atleast one cell may be written to the second unidirectional FIFO bufferfrom the first unidirectional FIFO buffer over a first enableddiagnostic loop. Furthermore, at least one cell may be written to thefirst unidirectional FIFO buffer from the second unidirectional FIFObuffer over a second enabled diagnostic loop.

FIG. 37 is a timing diagram of a processor port of one embodiment. Theprocessor port is in the read port clock domain. Once the grant signaland the request signal are active, the processor port read address issubstituted for the read port address. After the read is complete, theaddress register is switched back to the read port address.

In arbitrating slave module requests, the CBM performs arbitration onthe requests from the eight slave modules based on a minimum guaranteebandwidth which is set by the ACP for each slave module. A particularslave module will get higher priority if it is not providing thecorresponding minimum guarantee bandwidth.

In one embodiment, fair rate-based cell traffic arbitration is providedbetween eight traffic sources in the form of eight cell bus servicemodules on the same cell bus, but the embodiment is not so limited. Aprocessor can program the CBC of one embodiment with an 8-bit RelativeService Delay (RSD) value for each of the eight service Modules. ThisRSD value determines the portion of the total bandwidth of the switchplatform reserved for the respective service module. Given the bandwidthrequirement for each of the eight service modules, the corresponding RSDvalues can be calculated using the formula${{RSDi} = \frac{\frac{1}{BWi}}{\sum\limits_{n = 1}^{8}\quad \frac{1}{BWn}}},$

wherein RSDi is the relative service delay for the ith service module,and BWi is the bandwidth requirement for the ith service module. In oneembodiment, a bandwidth allocation for a service module is performedaccording to the formula${{BWi} = \frac{\frac{1}{RSDi}}{\sum\limits_{n = 1}^{8}\quad \frac{1}{RSDi}}},$

wherein RSDi is the RSD value for the service module, but the embodimentis not so limited. If the bandwidth is under-subscribed, the remainingbandwidth is shared among all eight service modules according to the RSDvalue of each service module. If the bandwidth is over-subscribed, eachservice module will have the assigned bandwidth portion decreasedaccording to the RSD values.

The rate-based cell traffic arbitration scheme of one embodiment is toanalogous to a parallel resistor network comprising eight resistors.FIG. 38 is a bandwidth distribution of one embodiment using a parallelresistor network model. The current 3802 flowing into the resistornetwork 3804 can be thought of as the total bandwidth supported by theCBM. The resistance value of each resistor 3810-3824 can be thought ofas the RSD value for each service module. The current that flows acrosseach resistor can be thought of as the portion of the total bandwidthallocated for the service module.

In operation, each service module comprises an 8-bit RSD register thatis configured by the system processor, or ACP, using the RSD value. Thevalue for each RSD is calculated based on the bandwidths allotted foreach service module. Furthermore, each service module uses an 8-bitService Delay Accumulator (SDA) register. The SDA register of eachservice module is configured using the SDA value, wherein the SDAregister keeps track of when each of the service modules should receiveservice.

The SDA value is calculated at each cell bus frame time for each of theservice modules based on the RSD value for each of the service modules,a request for service, and the minimum SDA value among the servicemodules during a cell bus frame time. In one embodiment, arbitrationlogic searches the SDA values of each of the service modules for aminimum SDA value, wherein the service module having the minimum SDAvalue and requesting service is selected for service. The SDA registerof the service module having the minimum SDA value is configured withthe RSD value when the service module is serviced. Each of the SDAregisters of each of the service modules that do not have the minimumSDA value are configured with the result of the SDA value of the servicemodule minus the minimum SDA value. In one embodiment, the SDA value iscalculated for each clock cycle, but the embodiment is not so limited.

FIG. 39 is a flowchart for providing cell traffic arbitration in aswitch platform of one embodiment. Operation begins at step 3902, atwhich at least one cell bus controller is programmed with at least onedelay value for each of a number of service modules. The delay valuedetermines a portion of a total bandwidth of the switch platformreserved for each of the service modules. The delay value comprises arelative service delay (RSD) value and a service delay accumulator (SDA)value, but the embodiment is not so limited. An 8-bit RSD register ofeach of the service modules is configured, at step 3904, using the RSDvalue. An 8-bit SDA register of each of the service modules isconfigured, at step 3906, using the SDA value, wherein the SDA registerkeeps track of when each of the plurality of service modules receivesservice. A determination is made, at step 3908, as to a portion of thetotal switch bandwidth to be reserved for each service module. When thetotal switch bandwidth is under-subscribed, the remaining bandwidth isshared among the number of service modules. When the total switchbandwidth is over-subscribed, a portion of the total bandwidth allocatedto at least one service module is decreased according to the RSD value.

The SDA value is calculated for each of the service modules at each cellbus frame time based on the RSD value for each of the service modules, arequest for service, and the minimum SDA value among the service modulesduring a cell bus frame time. The SDA values of each of the servicemodules are then searched for a minimum SDA value, wherein the servicemodule having the minimum SDA value and requesting service is selectedfor service. The SDA register of the service module having the minimumSDA value is configured with the RSD value when the service module isserviced. Each of the SDA registers of each of the service modules thatdo not have the minimum SDA value are configured with the result of theSDA value of the service module minus the minimum SDA value.

The CBC of one embodiment comprises diagnostic logic that assists incarrying out diagnostic functions. The diagnostic logic supportedcomprises: an interface loopback; a cell bus master-slave loopback,wherein a CBS loops back to any one CBM in the ingress direction, andthe same selected CBM loops back to a CBS in the egress direction; anindividual cell bus loopback; and an enable control for individualmodules and functions.

FIG. 40 is a block diagram of an interface loopback of one embodiment.When the interface loopback mode is enabled, incoming cells will not beprocessed by the CBC but, instead, will be looped back from the ECIC4002 to the ICOC 4004 and be sent back to the QE. Parity checking ofincoming cells will be performed in the ECP 4003.

FIG. 41 is a block diagram of an individual cell bus loopback of oneembodiment. When the individual cell bus loopback is selected, each cellbus will loopback onto itself. Basically, the cell from the ECP 4102will be looped back to the ICP 4104. When this loopback is selected,five cell buses go into loopback together.

Several functions of the CBC may be disabled in order to stop celltraffic through the CBC. Cell traffic is stopped so that the CBM and CBSFIFOs and queues can be monitored for cell progression through the CBC.The following modules and functions may be selectively disabled, but theembodiment is not so limited: the transmission of cells to the QEs bythe ICOC; the transmission of cells to the ICOC by the MCE; thetransmission of cell bus cells from the CBMs to the corresponding cellbuses; and, the transmission of cell bus cells from the CBS to the slavecell bus.

While the present invention has been described with reference tospecific exemplary embodiments, it will be evident that variousmodifications and changes may be made to these embodiments withoutdeparting from the broader spirit and scope of the invention as setforth in the claims. Accordingly, the specification and drawings are tobe regarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. An apparatus for providing cell bus management ina switch platform, the apparatus comprising: at least one master and atleast one slave bidirectional first-in-first-out (FIFO) unit, eachbidirectional FIFO unit comprises a first and a second unidirectionalFIFO buffer, each unidirectional FIFO buffer having a write port, thewrite port for each of the first and second unidirectional FIFO buffersis to output a write port cell count indicating if the first or secondunidirectional FIFO buffers is able to accept a cell.
 2. The apparatusof claim 1, wherein the at least one master bidirectional FIFO unit isto cease reading at least one cell from the second unidirectional FIEFObuffer of the at least one slave bidirectional FIFO unit in response tothe write port cell count of the second unidirectional FIFO buffer. 3.The apparatus of claim 1, wherein the at least one master bidirectionalFIFO unit is to disable at least one switch in the switch platform fromrouting at least one cell to the at least one slave bidirectional FIFOunit in response to the write port cell count of the secondunidirectional FIFO buffer.
 4. The apparatus of claim 3, wherein the atleast one switch in the switch platform is to route the at least onecell to another slave bidirectional FIFO unit in response to the writeport cell count of the second unidirectional FIFO buffer.
 5. Theapparatus of claim 2, wherein the at least one master bidirectional FIFOunit is to resume reading the at least one cell from the secondunidirectional FIFO buffer of the at least one slave bidirectional FIFOunit in response to the write port cell count of the secondunidirectional buffer.
 6. The apparatus of claim 1, wherein the at leastone master bidirectional FIFO unit is to enable at least one switch inthe switch platform to route at least one cell to the at least one slavebidirectional FIFO unit in response to the write port cell count of thesecond unidirectional buffer.
 7. The apparatus of claim 1, wherein theat least one slave bidirectional FIFO unit is programmed to output thewrite port cell count at a certain count value.
 8. The apparatus ofclaim 1, wherein one master bidirectional FIFO unit is coupled to eightslave bidirectional FIFO units.
 9. The apparatus of claim 1, whereineach unidirectional FIFO buffer includes asynchronous read and writeports.
 10. The apparatus of claim 1, wherein the write port of eachunidirectional FIFO buffer is to output a status indicating spaceavailable in the unidirectional buffer for at least one more cell. 11.The apparatus of claim 10, wherein the at least one master bidirectionalFIFO unit is to cease reading at least one cell from the secondunidirectional FIFO buffer of the at least one slave bidirectional FIFOunit in response to the status indicating space available in theunidirectional buffer for at least one more cell.
 12. The apparatus ofclaim 10, wherein the at least one master directional FIFO unit is todisable at least one switch in the switch platform from routing at leastone cell to the at least one slave bidirectional FIFO unit in responseto the status indicating space available in the unidirectional bufferfor at least one more cell.
 13. The apparatus of claim 12, wherein theat least one switch in the switch platform is to route the at least onecell to another slave bidirectional FIFO unit in response to the statusindicating space available in the unidirectional buffer for at least onemore cell.
 14. The apparatus of claim 11, wherein the at least onemaster bidirectional FIFO unit is to resume reading the at least onecell to the second unidirectional FIFO buffer of the at least one slavebidirectional FIFO unit in response to the status indicating spaceavailable in the unidirectional buffer for at least one more cell. 15.The apparatus of claim 10, wherein the at least one master bidirectionalFIFO unit is to enable at least one switch in the switch platform toroute at least one cell to the at least one slave bidirectional FIFOunit in response to the status indicating space available in theunidirectional buffer for at least one more cell.
 16. The apparatus ofclaim 1, wherein each unidirectional PFIO buffer includes a read port,the read port is to output a read port cell count, and wherein theunidirectional FIFO buffer is to output a status indicating spaceavailable in the unidirectional FIFO buffer for at least one more cell.17. The apparatus of claim 1, wherein a cell size and a word size ofeach unidirectional FIFO buffer is programmable.
 18. The apparatus ofclaim 1, wherein the at least one bidirectional FIFO unit is to write atleast one cell to and read at least one cell from at least oneasynchronous transfer mode (ATM) interface, at least one frame relayinterface, at least one voice interface, at least one data interface,and at least one switch interface.
 19. The apparatus of claim 1, whereinthe first unidirectional FIFO buffer is to read at least one cell fromat least one switch in the switch platform, wherein the at least oneswitch is to handle cells from sources having a plurality of bandwidths.20. The apparatus of claim 19, wherein the at least one switch is toroute the at least one cell to an OC12 trunk line and to at least oneservice module.
 21. The apparatus of claim 20, wherein the at least oneservice module is to provide the at least one cell to at least oneservice subscriber using T1, E1, T3, E3, OC3, and OC 12 ports.
 22. Theapparatus of claim 1, wherein the at least one bidirectional FIFO unitcomprises a diagnostic interface, wherein the diagnostic interface is tosupport a non-destructive read of the at least one bidirectional FIFOunit if at least one cell is being written to and read from the at leastone bidirectional FIFO unit.
 23. The apparatus of claim 1, wherein theat least one cell is to be written to the second unidirectional FIFObuffer from the first unidirectional FIFO buffer over a first enableddiagnostic loop.
 24. The apparatus of claim 9, wherein a write portlogic of each unidirectional FIFO buffer is synchronous with a writeclock, and wherein a read port logic of each unidirectional FIFO bufferis synchronous with a read clock.
 25. The apparatus of claim 1, whereinat least one invalid cell can be discarded from each unidirectional FIFObuffer.
 26. A network switch platform comprising: at least one servicemodule; at least one cell bus controller coupled among the at least oneservice module and at least one switch; at least one slave bidirectionalfirst-in-first-out (FIFO) unit located in the at least one servicemodule; and at least one master bidirectional FIFO unit located in theat least one cell bus controller, wherein each bidirectional FIFO unitcomprises a first and a second unidirectional FIFO buffer, wherein thesecond unidirectional FIFO buffer of the at least one slavebidirectional FIFO unit includes a write port, the write port is tooutput a write port cell count and a status indicating space availablein the second unidirectional FIFO buffer for at least one more cell,wherein the at least one slave bidirectional FIFO unit is programmed tooutput the write port cell count from the write port of the secondunidirectional FIFO buffer at a certain count value.
 27. The networkswitch platform of claim 26, wherein the at least one masterbidirectional FIFO unit is to cease reading at least one cell from thesecond unidirectional FIFO buffer of the at least one slavebidirectional FIFO unit in response to the write port cell count,wherein the at least one master bidirectional FIFO unit is to disable atleast one switch from routing at least one cell to the at least oneslave bidirectional FIFO unit in response to the write port cell count,wherein the at least one switch is to route the at least one cell toanother of the at least one slave bidirectional FIFO units in responseto the write port cell count.
 28. The network switch platform of claim27, wherein the at least one master bidirectional FIFO unit is to resumereading at least one cell from the second unidirectional FIFO buffer ofthe at least one slave bidirectional FIFO unit in response to the writeport cell count, wherein the at least one master bidirectional FIFO unitis to enable the at least one switch to route at least one cell to theat least one slave bidirectional FIFO unit in response to the write portcell count.
 29. The network switch platform of claim 26, wherein the atleast one master bidirectional FIFO unit is to cease reading at leastone cell from the second unidirectional FIFO buffer of the at least oneslave bidirectional FIFO unit in response to the status indicating spaceavailable in the unidirectional buffer for at least one more cell,wherein the at least one master bidirectional FIFO unit is to disable atleast one switch from routing at least one cell to the at least oneslave bidirectional FIFO unit in response to the status indicating spaceavailable in the unidirectional buffer for at least one more cell,wherein the at least one switch is to route the at least one cell toanother of the at least one slave bidirectional FIFO units in responseto the status indicating space available in the unidirectional bufferfor at least one more cell.
 30. The network switch platform of claim 29,wherein the at least one master bidirectional FIFO unit is to resumereading at least one cell from the second unidirectional FIFO buffer ofthe at least one slave bidirectional FIFO unit in response to the statusindicating space available in the bidirectional buffer for at least onemore cell, wherein the at least one master bidirectional FIFO unitenables the at least one switch to route at leas tone cell to the atleast one slave bidirectional FIFO unit in response to the statusindicating space available in the unidirectional buffer for at least onemore cell.
 31. The network switch platform of claim 26, wherein eachunidirectional FIFO buffer is to output a read port cell count, eachunidirectional FIFO buffer includes a read port to output a statusindicating space available in the unidirectional FIFO buffer for atleast one more cell.
 32. The network switch platform of claim 26,wherein a cell size and a word size of the first and secondunidirectional FIFO buffers are programmable.
 33. The network switchplatform of claim 26, wherein each of the at least one bidirectionalFIFO units is coupled to write at least one cell from and read at leastone cell to at least one asynchronous transfer mode (ATM) interface, atleast one frame relay interface, at least one voice interface, at leastone data interface, and at least one switch interface.
 34. The networkswitch platform of claim 26, wherein each unidirectional FIFO buffercomprises asynchronous read and write ports, write port logic, and readport logic, and wherein the write port logic is synchronous with a writeclock, and wherein the read port logic is synchronous with a read clock.35. The network switch platform of claim 26, further comprising at leastone diagnostic interface, wherein the at least one diagnostic interfaceis to support a non-destructive read of at least one bidirectional FIFOunit if at least one cell is being written to and read from the at leastone bidirectional FIFO unit.
 36. A method for providing cell busmanagement in a network switch, the method comprising: programming acell count value to determine if a first slave bidirectional FIFO unitis to output a write port cell count from a write port; outputting thewrite port cell count from the first slave bidirectional FIFO unit ifthe write port cell count of the first slave bidirectional FIFO unit isto exceed the programmed cell count value; and suspending reading of atleast one cell from the first slave bidirectional FIFO unit in responseto the write port cell count.
 37. The method of claim 36, furthercomprising: routing the at least one cell to a second slavebidirectional FIFO unit in response to the write port cell count;reading the at least one cell from the second slave bidirectional FIFOunit in response to the write port cell count; disabling the routing ofthe at least one cell to the second slave bidirectional FIFO unit inresponse to the write port cell count; and resuming reading of the atleast one cell to the first slave bidirectional FIFO unit in response tothe write port cell count.
 38. The method of claim 36, furthercomprising: outputting a read port cell count; and outputting from atleast one read port a status indicating space available in aunidirectional FIFO buffer for at least one more cell.
 39. The method ofclaim 36, further comprising: programming a cell size of each of theslave bidirectional FIFO units; and programming a word size of each ofthe slave bidirectional FIFO units.
 40. The method of claim 37, furthercomprising: synchronously writing at least one cell from at least oneport to at least one bidirectional FIFO unit, when rein the at least oneport is coupled to at least one source having at least one bandwidth;asynchronously transferring the at least one cell through the at leastone bidirectional FIFO unit; and synchronously reading the at least onecell from the at least one bidirectional FIFO unit to the at least oneport.
 41. The method of claim 40, wherein the at least one portcomprises at least one asynchronous transfer mode (ATM) interface, atleast one frame relay interface, at least one voice interface, at leastone data interface, at least one switch interface, at least one OC12interface, and at least one OC3 interface.
 42. The method of claim 37,further comprising: discarding at least one invalid cell from eachbidirectional FIFO unit; and executing a non-destructive read of the atleast one bidirectional FIFO unit if at least one cell is being writtento and read from the at least one bidirectional FIFO unit.
 43. A methodfor providing cell bus management in a network switch, the methodcomprising: outputting a status indicating space available for at leastone more cell from a write port of a first slave bidirectional FIFO unitif a cell count of the first slave bidirectional FIFO unit is to exceedone; and suspending reading of at least one cell from the first slavebidirectional FIFO unit in response to the outputted status.
 44. Themethod of claim 43, further comprising: routing the at least one cell toa second slave bidirectional FIFO unit in response to the status;reading the at least one cell to the second slave bidirectional FIFOunit in response to the status; disabling the routing of the at leastone cell to the second slave bidirectional FIFO unit in response to thestatus; and resuming reading of the at least one cell to the first slavebidirectional FIFO unit in response to the status.
 45. A switchplatform, comprising: at least one bidirectional buffering unit, the atleast one bidirectional buffering unit including: a first and secondunidirectional buffer, each unidirectional buffer having a write port tooutput a write port cell count indicating if the unidirectional bufferis able to receive cells.
 46. The switch platform of claim 45, whereinthe at least one bidirectional buffering unit is a first-in-first-out(FIFO) buffering unit.
 47. The switch platform of claim 45, wherein thefirst and second unidirectional buffers are unidirectional FIFO buffers.